2.1. Sampling and isolation
Water samples were collected from five different locations;
three fresh water lakes (Lac Croche (4559024.3700N 74
0021.0100W) and Lac Pilon (460014.0200N 74107.0900W), University
of Montreal biological station (4559017.1100N 740020.5500W)), situated
in the Laurentian region north of Montreal, Canada; and two
on each side of the Saint Lawrence river, situated approximately
10 km downstream from the confluence with the Ottawa river,
where the water of both rivers are not yet totally mixed
(4525039.1200N 7349015.7800W and 4521023.3600N 7348049.9600W).
Sampling at each site was conducted during the spring, summer
and fall. Coarse material, potentially including zooplankton, was
removed on site by filtration through a 50 lm mesh net and then
samples were stored in cool boxes for transportation to the laboratory.
Once in the laboratory, the water samples were filtered
through a series of membranes of decreasing mesh size (33, 20
and 0.45 lm). The retention products of each membrane was taken
using a sterile swab, and directly plated on BBM agar plates
(Andersen, 2005) and incubated in a light chamber at 20 ± 2 C.
In all the experiments reported in this study, no special provisions
were made for CO2 supply. Thus, all cultivations were with
atmospheric CO2. Light was provided by warm white fluorescent
bulbs at 25 W/m2 operated on a light/dark cycle of 12/12 h. After
growth, different colonies were inoculated in 125 ml Erlenmeyer
flasks containing 70 ml of BBM medium and incubated in a light
mounted shaker at 20 ± 2 C, with shaking at 120 RPM and a light
intensity of 21.2 W/m2 using a photoperiod of 12 h light: dark.
Isolates were then kept in falcon tubes with the same medium
for the further analysis.